1. Technical Field
The present disclosure relates to linear light-emitting diode (LED) lamps that work with linear tube lamp fixtures configured to electrically connect either instant-start electronic ballast or the AC mains, and more particularly to a universal, shock and fire hazard-free linear LED tube lamp with a shock-protection mechanism.
2. Description of the Related Art
Solid-state lighting from semiconductor light-emitting diodes (LEDs) has received much attention in general lighting applications today. Because of its potential for more energy savings, better environmental protection (with no hazardous materials used), higher efficiency, smaller size, and longer lifetime than conventional incandescent bulbs and fluorescent tubes, the LED-based solid-state lighting will be a mainstream for general lighting in the near future. Meanwhile, as LED technologies develop with the drive for energy efficiency and clean technologies worldwide, more families and organizations will adopt LED lighting for their illumination applications. In this trend, the potential safety concerns such as risk of electric shock and fire become especially important and need to be well addressed.
In today's retrofit application of a linear LED tube (LLT) lamp to replace an existing fluorescent tube, consumers may choose either to adopt a ballast-compatible LLT lamp with an existing ballast used to operate the fluorescent tube or to employ an AC mains-operable LED lamp by removing/bypassing the ballast. Either retrofit application has its advantages and disadvantages. In the former case, although the ballast consumes extra power, it is straightforward to replace the fluorescent tube without rewiring, which consumers have a first impression that it is the best alternative to fluorescent tube lamps. But the fact is that total cost of ownership for this approach is high regardless of very low initial cost. For example, the ballast-compatible LLT lamps work only with particular types of ballasts. If the existing ballast is not compatible with the ballast-compatible LLT lamp, the consumer will have to replace the ballast. Some facilities built long time ago incorporate different types of fixtures, which requires extensive labor for both identifying ballasts and replacing incompatible ones. Moreover, a ballast-compatible LLT lamp can operate longer than the ballast. When an old ballast fails, a new ballast will be needed to replace in order to keep the ballast-compatible LLT lamps working. Maintenance will be complicated, sometimes for lamps and sometimes for ballasts. The incurred cost will preponderate over the initial cost savings by changeover to the ballast-compatible LLT lamps for hundreds of fixtures throughout a facility. When the ballast in a fixture dies, all the ballast-compatible tube lamps in the fixture go out until the ballast is replaced. In addition, replacing a failed ballast requires a certified electrician. The labor costs and long-term maintenance costs will be unacceptable to end users. From energy saving point of view, a ballast constantly draws power, even when the ballast-compatible LLT lamps are dead or not installed. In this sense, any energy saved while using the ballast-compatible LLT becomes meaningless with the constant energy use by the ballast. In the long run, ballast-compatible LLT lamps are more expensive and less efficient than self-sustaining AC mains-operable LLT lamps.
On the contrary, an AC mains-operable LLT lamp does not require a ballast to operate. Before use of an AC mains-operable LLT lamp, the ballast in a fixture must be removed or bypassed. Removing or bypassing the ballast does not require an electrician and can be replaced by end users. Each AC mains-operable LLT lamp is self-sustaining. If one AC mains-operable tube lamp in a fixture goes out, other lamps in the fixture are not affected. Once installed, the AC mains-operable LLT lamps will only need to be replaced after 50,000 hours. In view of above advantages and disadvantages of both ballast-compatible LLT lamps and AC mains-operable LLT lamps, it seems that market needs a most cost-effectively solution by using a universal LLT lamp that can be used with the AC mains and is compatible with an electronic ballast so that LLT lamp users can save an initial cost by changeover to such a universal LLT lamp followed by retrofitting the lamp fixture to be used with the AC mains when the ballast dies. Electronic ballasts have several different types. However in the US, instant-start electronic ballasts are most popular in lamp fixtures because they are more efficient and less expensive than other types of electronic ballasts and have few wires for installation. In this sense, the instant-start electronic ballast is emphasized in the present disclosure although the electronic ballast will be used hereafter to represent the instant-start electronic ballast for simplicity.
The AC mains-operable LLT lamp does not need a high voltage to ionize the gases inside the gas-filled fluorescent tube before sustaining continuous lighting. However, such LLT lamps operating at the AC mains, 110, 220, or 277 VAC, have one construction issue related to product safety and needed to be resolved prior to wide field deployment. This kind of LLT lamps always fails a safety test, which measures through lamp leakage current. Because the line and the neutral of the AC mains apply to both opposite ends of the tube when connected, the measurement of current leakage from one end to the other consistently results in a substantial current flow, which may present a risk of shock during re-lamping. Due to this potential shock risk to the person who replaces LLT lamps in an existing fluorescent tube fixture, Underwriters Laboratories (UL) uses its standard, UL 935, Risk of Shock During Relamping (Through Lamp), to do a current leakage test and to determine if LLT lamps under test meet the consumer safety requirement.
In the U.S. patent application Ser. No. 14/135,116, filed Dec. 19, 2013, two double shock protection switches and a degenerate voltage sensing and control mechanism are adopted in an LLT lamp such that AC power from any two pins of four pins in the LLT lamp can operate the lamp without operational uncertainty and fire or shock hazards due to misapplications of a power supply connection. In other words, no matter what a lamp fixture is configured as single-ended or double-ended, the LLT lamp automatically detects it and works for either configuration. However, such an LLT lamp can only operate with the AC mains and is not compatible with an electronic ballast.
FIGS. 1 and 2 respectively depict an AC mains-operable LLT lamp installed in double-ended and single-ended fixture lamp holders. The LLT lamp 300 comprises a housing having two ends; two lamp bases 660 and 760 having respective bi-pins 250 and 350 at each end of the housing; two actuation mechanisms 640 and 740 of shock protection switches 610 and 710 in the two lamp bases 660 and 760, respectively; two degenerate voltage sensing and control devices; an LED driver 400 having two inputs; and LED arrays 214 on an LED PCB. Essentially the degenerate voltage sensing and control devices are embodied in two bridge rectifiers 603 and 604, wherein each bridge rectifier comprises four diodes. The two bridge rectifiers 603 and 604 are connected to an LED driver 400 in parallel such that the positive and the negative input/output ports 503 and 504 of the first bridge rectifier 603 respectively connect to the positive and the negative input/output ports 505 and 506 of the second bridge rectifier 604. Furthermore, the eight diodes in the two bridge rectifiers are partially paired to perform a full wave rectification of the AC voltage from the AC mains according to single-ended or double-ended wiring configuration in the lamp fixture.
A diode conducts an electric current if it is forward biased but blocks a current flow if it is reverse biased. Taking advantage of this property, each diode in the bridge rectifiers 603 and 604 can sense an electric potential difference between its two ports and convert AC to DC if an AC voltage is applied to a circuit with a diode connected in a proper manner. With the eight diodes configured in FIG. 1 and FIG. 2, the two bridge rectifiers 603 and 604 can control the electric current flows to the LED driver and the electric current return, thus delivering a power to the LED driver.
In FIG. 1, when the lamp bases 660 and 760 are respectively installed in the fixture lamp holders 810 and 820, the actuation mechanisms 640 and 740 are actuated to turn on both sets of electrical contacts on the shock protection switches 610 and 710. The diodes 611 and 612 in the bridge rectifier 603 detect an electric current path and conduct a positive cycle of an electric current from the socket 255 of the fixture lamp holder 810 (where “L” of the AC mains is designated), the electrical contacts 401 and 403, the input/output ports 402 and 404, the diodes 611 and 612, the input/output port 503, the first input 501 of the LED driver 400 to the LED driver 400, returned from the LED driver 400, through the second input 502 of the LED driver 400, the input/output port 506, the diodes 617 and 618, and the electrical contacts 405 and 407 to “N” of the AC mains, thus delivering a power to the LED driver 400. In this electric current path, the diodes 611 and 612, 617, and 618 are forward biased whereas the diodes 613, 614, 615, and 616 are reverse biased, so the electric current can go through a correct path from “L” to “N” of the AC mains. Similarly for a negative cycle except that the diodes 613, 614, 615, and 616 are forward biased whereas the diodes 611, 612, 617, and 618 are reverse biased, an electric current can start from the fixture lamp holder 820, the diodes 615 and 616, the input/output port 505, the first input 501 of the LED driver 400 to the LED driver 400, returned from the LED driver 400, through the second input 502 of the LED driver 400, the input/output port 504, the diodes 613 and 614 to the fixture lamp holder 810, thus delivering a power to the LED driver 400. In FIG. 1, any electric current will not leak out from the exposed bi-pins because once, for example, the lamp base 660 is out of the socket of the lamp holder 810, the actuation mechanism 640 will be deactivated, turning off the switch 610, thus disconnecting the electric current—no electric shock hazard. Similarly for the lamp base 760, when the lamp base 760 is out of the socket of the lamp holder 820, the actuation mechanism 740 is deactivated, turning off the switch 710, thus disconnecting the electric current from flowing out to electrically shock an installer.
In FIG. 2, the LLT lamp 300 is installed in a single-ended fixture in such a way that the lamp bases 660 and 760 respectively connect to the fixture lamp holders 910 and 920, to which “L” and “N” of the AC mains are respectively connected. The actuation mechanisms 640 and 740 are actuated to turn on both sets of electrical contacts on the shock protection switches 610 and 710. The diode 611 in the bridge rectifier 603 detects an electric current path and conduct a positive cycle of an electric current from the socket 255 (where “L” of the AC mains is designated) in the fixture lamp holder 910, the electrical contact 401, the input/output port 402, the diode 611, the input/output port 503, the first input 501 of the LED driver 400 to the LED driver 400, returned from the LED driver 400, through the second input 502 of the LED driver 400, the input/output port 504, the diode 614, the input/output port 404, and the electrical contact 403, to the socket 256 (where “N” of the AC mains is designated) in the fixture lamp holder 910, thus delivering a power to the LED driver 400. In this case, the diodes 611 and 614 are forward biased whereas the diodes 612 and 613 are reverse biased, so the electric current can go through a correct path from “L” to “N” of the AC mains. Similarly for a negative cycle except that the diodes 612 and 613 are forward biased whereas the diodes 611 and 614 are reverse biased, an electric current can start from the socket 256 in the fixture lamp holder 910, the electrical contact 403, input/output port 404, the diode 612, the input/output port 503, the first input 501 of the LED driver 400 to the LED driver 400, returned from the LED driver 400, through the second input 502 of the LED driver 400, the input/output port 504, the diode 613, the input/output port 402, and the electrical contact 401, to the socket 255 in the fixture lamp holder 910, thus delivering the negative cycle of the power to the LED driver 400.
When the two pins of bi-pin in the lamp base 660 of the LLT lamp 300 are first inserted into the sockets 255 and 256 of the fixture lamp holder 910, the LED driver 400 immediately obtains a power via the bridge rectifier 603 no matter whether the lamp base 760 is installed in the fixture lamp holder 920 or not. However, the electric current returned from the LED driver 400 can flow from the input/output port 506, the diodes 617 and 618 in the bridge rectifier 604 to the two pins of the bi-pin 350 in the lamp base 760. If there is no shock protection switch 710 along the path in between the input/output ports 406 and 408 and the two pins of the bi-pin 350, when the two pins of the bi-pin 350 are exposed, the leakage current can flow out, creating an electric shock hazard if an installer touches the bi-pin 350. Therefore, the shock protection switch 710 and the actuation mechanism 740 in place can prevent the electric shock hazard from happening because only when the lamp base 760 is installed in the fixture lamp holder 920, is the actuation mechanism actuated to turn on the switch 710. Although “L” and “N” are connected to the lamp base 660 in FIG. 2, the LLT lamp 300 can still operate when the AC mains connect to the lamp base 760 rather than the lamp base 660 because the two bridge rectifiers 603 and 604 are connected to the LED driver 400 in parallel through the two inputs 501 and 502 of the LED driver 400, and the two bridge rectifiers 603 and 604 are symmetric at the two ends of the LLT lamp. Similarly for double-ended linear fixtures, when “L” and “N” shown in FIG. 1 are exchanged, the LLT lamp can still operate. The embodiments depicted in FIGS. 1 and 2 have an advantage of being simple and also passive without pre-power to operate. Thus, it is easy to implement.
Misapplications of power supply connections for conventional LLT lamps that substitute for linear fluorescent lamps are main causes of fire and electric shock hazards today, where the conventional LLT lamps are incorrectly connected to a supply source, the lamp base is either inserted incorrectly into a lamp holder or inserted into a lamp holder not intended for the conventional LLT lamp, or a conventional LLT lamp is connected to lamp holders with supply connections that do not match the lamp configuration. All of these misapplications may result in fire and shock hazards.
To completely remove these hazards from conventional LLT lamps, manufacturers need to ensure at first no electrically shorted ends in either single-ended or double-ended LLT lamps. For double-ended LLT lamps that operate in an AC-mains configuration, double protection switches on both ends of the LLT lamps must be used without compromise, the same for the lamps operable in both double-ended and single-ended fixtures. Whereas a lamp fixture may be wired single-ended or double-ended with the AC mains, or wired for operating with an electronic ballast, an LLT lamp may be configured internally in the similar fashion. However, any incompatible combinations of the conventional LLT lamps and the fixtures lead to failure of operation. These kinds of operational uncertainty, inconvenience, and possible hazards may severely affect the willingness of the consumers to adopt conventional LLT lamps. Therefore, it is believed that a universal LLT lamp is needed to work not only with the AC mains but also with an electronic ballast without uncertainty and hazards when installed in either single-ended or double-ended fixtures during initial installation or during lamp replacement when the above-mentioned misapplications may occur.